1. Field of the Invention
The present invention relates to a resin-coated metal plate used as a protective back plate for efficiently obtaining high-quality products in drilling as one of steps of manufacturing a printed wiring board, and a method of drilling a printed wiring board using the resin-coated metal plate.
2. Description of the Related Art
The printed wiring board is for mounting electronic components and electrically connecting between the electronic components, and extremely important as an internal component of an electric product. In manufacturing the printed wiring board, as one of steps of manufacturing the board, there is a step of forming through-holes in a sectional direction in order to enable current supply between the uppermost layer and the lowermost layer of the printed wiring board. The through-holes are indispensable for the printed wiring board, and typically the number of the through-holes is large, therefore the drilling step holds an important position in manufacturing the printed wiring board.
While the printed wiring board generally includes a composite material formed by alternately stacking conductor layers including a copper foil, and insulating layers including glass woven fabric cloth in which epoxy resin or the like is impregnated and cured, physical properties are different between the material configuring the conductor layers and the material configuring the insulating layers. Therefore, there is a difficulty that defects such as boundary separation between the conductor layer and the insulating layer, or a crack tend to occur during drilling with a drill, causing deterioration in surface roughness of a inner wall of a through-hole, or wear or breakage of a drill, that is, a bad effect is induced on drilling with a drill due to the difference in physical properties. Moreover, since periodical irregularity due to irregularity of the insulating layer (glass fiber cloth) exists on a surface of the printed wiring board, positional accuracy tends to be degraded during drilling with a drill. Furthermore, there is a difficulty that resin in the printed wiring board is softened due to heat generated during drilling with a drill, and formed into a stain so-called smear which is easily adhered on the conductor layer (copper foil), leading to a factor of insufficient electrical conduction after through-hole plating.
In particular, with recent size reduction and improvement in accuracy of electronic devices, a drilled hole (through-hole) provided in the printed wiring board is advanced in reduction in diameter or increase in density, and a technique is now indispensable, the technique enabling formation of a drilled hole having a smooth-inner wall at a more accurate position. Furthermore, reduction in manufacturing cost is increasingly demanded from a recent economical situation, consequently a more efficient production technology of the printed wiring board is intensively required to be established.
To overcome the difficulty, as a technique for enabling suppression of heat generation during drilling, U.S. Pat. No. 4,781,495 and U.S. Pat. No. 4,929,370 disclose a method in which a sheet impregnated with aqueous lubricant is disposed on one side or two sides of a laminated board, then the laminated board is subjected to drilling using the sheet impregnated with aqueous lubricant as a back plate. In the sheet impregnated with aqueous lubricant used in such a drilling method, a mixture of glycol such as diethylene glycol or dipropylene glycol as a solid aqueous lubricant, synthesized wax such as fatty acid, and nonionic surfactant are impregnated in a porous material such as paper.
JP-A-2002-120198 discloses a method in which an aqueous-resin-coated metal plate, which is formed by adhering a mixture of polyethylene glycol-dimethyl terephthalate polycondensation and polyoximethylene monostearate, either of which is an aqueous compound, on one side of an aluminum plate is used as a back plate for drilling with a drill.
JP-A-2001-150215 discloses a method in which a sheet is piled on a printed wiring board for drilling, the sheet being formed by pasting a thermoplastic resin film in a multilayer structure, which is formed by laminating a thermoplastic resin layer containing no slipping agent on the outside of a thermoplastic resin layer containing a slipping agent, and a metal foil together. JP-A-2001-246696 and JP-A-2000-218599 disclose a sheet is formed by laminating a polyester resin composition, including thermoplastic polyester resin mixed with inorganic filler and/or aqueous slipping agent, and a metal foil, and a drilling method using the sheet. Furthermore, JP-B-7-50831 discloses a method of disposing a thermoplastic film having a melting temperature of 100 to 150° C. directly on a copper foil as a method of manufacturing a printed wiring board.